Highlights From the North American Society for the Study of Obesity Annual Meeting: A Physician's View

Raymond A. Plodkowski, MD


December 01, 2003

In This Article

Controversies Regarding Diet Compositions Used for Weight Loss

As overweight and obesity increases in the United States, people have turned to popular diets as well as evidence-based interventions. One of the greatest controversies involves low-carbohydrate diets, which receive enormous amounts of attention in the lay press. There is substantial debate regarding the safety and efficacy of these low-carbohydrate, high-protein diets. Several popular diets fall into this category (ranging from 27% to 34% protein content), including Atkins, the Zone, Protein Power, and Sugar Busters.[12,13,14,15]

Gary Foster, PhD, from the University of Pennsylvania, is one of the authors of a recent weight-loss study of the Atkins diet. He gave an overview at the NAASO meeting[16] of his study and the other 2 studies released in 2003 that addressed the safety and efficacy of low-carbohydrate diets.

The first study, by Brehm and colleagues,[17] compared a very low-carbohydrate diet and a calorie-restricted low-fat diet on body weight and cardiovascular risk factors in healthy women. Subjects were randomized to 6 months of either a very low-carbohydrate diet or a calorie-restricted diet with 30% of the calories as fat (a typical low-fat diet). The 42 women who completed the trial reduced calorie consumption by comparable amounts at 3 and 6 months. The very low-carbohydrate diet group lost more weight (8.5 ± 1.0 vs 3.9 ± 1.0 kg; P < .001) and more body fat (4.8 ± 0.67 vs 2.0 ± 0.75 kg; P < .01) than the low-fat diet group. The 2 groups had similar changes in plasma LDL-cholesterol and HDL-cholesterol levels. Similarly, the fasting glucose and insulin levels did not differ between the 2 study groups at the 3- or 6-month assessments.

The second study reviewed was from Samaha and colleagues.[18] Seventy-nine subjects completed the 6-month study. The study subjects followed a low-carbohydrate diet or a low-fat diet. Subjects on the low-carbohydrate diet lost more weight than those on the low-fat diet (-5.8±8.6 kg vs -1.9±4.2 kg; P = .002) and had greater decreases in triglyceride levels (mean, -20±43% vs -4±31%; P = .001). The LDL-cholesterol and HDL-cholesterol levels showed similar changes at 6 months. Insulin sensitivity, measured only in subjects without diabetes, also improved more among subjects on the low-carbohydrate diet (6±9% vs -3±8%, P = .01). The amount of weight lost (P < .001) and assignment to the low-carbohydrate diet (P = .01) were independent predictors of improvement in triglyceride levels and insulin sensitivity.

Dr. Foster's group performed the third study.[19] This 1-year trialstudied 63 obese male and female subjects who were randomly assignedto either a low-carbohydrate, high-protein, high-fat diet ora low-calorie, high-carbohydrate, low-fat diet. Subjects on the low-carbohydrate diet lost moreweight than subjects on the conventional diet at 3 months (-6.8 ± 5.0 vs -2.7 ± 3.7%of body weight; P = .001) and at 6 months (-7.0 ± 6.5vs -3.2 ± 5.6% of body weight, P = .02), butthe difference at 12 months was not significant (-4.4 ± 6.7vs -2.5 ± 6.3% of body weight, P = .26). These studies suggest that the low-carbohydrate/high-protein diets are safe in the short term and bring about greater weight loss than the traditional low-fat diet does at 6 months.

I would caution practitioners that the long-term safety of this class of diets has not been established. These diets are palatable and attractive over the short term and, therefore, have gained acceptance. Unfortunately, the composition of these diets usually relies on animal proteins that are often high in total fat, saturated fat, and cholesterol.[20] Therefore, frequent monitoring of fasting lipid panels are indicated. The diet should be discontinued if the lipid profile deteriorates, because the patient will be at higher risk for cardiac events. The initial weight loss seen in low-carbohydrate/high-protein diets is due to fluid loss related to reduced carbohydrate intake, overall caloric restriction, and ketosis-induced appetite suppression. An ongoing study sponsored by the National Institutes of Health hopes to answer some of the questions regarding the long-term safety of these diets. The study will include a total of 360 patients and includes multiple outcomes: renal function, bone density, exercise tolerance, endothelial function, and insulin sensitivity.


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